Communication apparatus

ABSTRACT

A communication apparatus includes a transmitter configured to supply an information signal as an electric field to a transmission medium; a receiver configured to detect the electric field through the transmission medium to acquire the information signal; an insulating casing that accommodates at least one of the transmitter and the receiver; and a filling member that is arranged at least one of between the casing and the transmitter and between the casing and the receiver.

CLAIM OF PRIORITY

This application is a Continuation of International Application No.PCT/JP2008/057520 filed on Apr. 17, 2008, which claims benefit ofJapanese Patent Application No. 2007-111317 filed on Apr. 20, 2007,which are hereby incorporated by reference. This application is alsorelated to Japanese Application No. 2008-542120 filed on Sep. 4, 2008,which is the National Phase Application of PCT/JP2008/057520, and nowJapanese Patent No. 4256468 registered on Feb. 6, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication apparatus used in acommunication system in which transmission and reception is performedthrough a transmission medium such as a human body.

2. Description of the Related Art

Due to recent developments in technology, communication methods in whichelectric fields are induced in the human body or the like (so-calledelectric field communication) have been proposed as totally newcommunication methods. An example of such a communication system isdisclosed, for example, in PCT Japanese Translation Patent PublicationNo. 11-509380. In the communication system, a transmitter supplies anelectric field corresponding to a modulation signal obtained bymodulating an information signal to a human body serving as atransmission medium, and a receiver detects the electric fieldtransmitted through the human body and performs demodulation to obtainthe original signal corresponding to the electric field.

In the electric field communication mentioned above, a signal istransmitted by capacitive coupling, instead of causing a through-currentto flow to a transmission medium. Thus, it is desirable that thecapacitive coupling between a transmission electrode and thetransmission medium, the transmission electrode providing a capacitivecoupling between the transmission medium and a transmission circuit of atransmitter, and the capacitive coupling between a reception electrodeand the transmission medium, the reception electrode providing acapacitive coupling between the transmission medium and a receptioncircuit of a receiver, be large.

However, in the case that the transmitter or receiver described above isprovided in the casing of an electronic apparatus such as a cellularphone, a space is formed between the internal surface of the casing andthe transmission electrode of the transmitter or between the internalsurface of the casing and the reception electrode of the receiver.Hence, the capacitive coupling between the transmission or receptionelectrode and a transmission medium is reduced, and a transmissionsignal thus becomes faint. Furthermore, due to a variation in the spacebetween the internal surface of the casing and the transmission orreception electrode, the signal intensity varies.

SUMMARY OF THE INVENTION

The present invention provides a communication apparatus including atransmitter or receiver for electric field communication and beingcapable of achieving reliable electric field communication.

A communication apparatus according to an aspect of the presentinvention includes a transmitter configured to supply an informationsignal as an electric field to a transmission medium; a receiverconfigured to detect the electric field through the transmission mediumto acquire the information signal; an insulating casing thataccommodates at least one of the transmitter and the receiver; and afilling member that is arranged at least one of between the casing andthe transmitter and between the casing and the receiver.

With this configuration, since the electrostatic capacitance between atransmission electrode and the transmission medium or between areception electrode and the transmission medium increases, signalattenuation can be reduced. In addition, since no air-gap is formedbetween the internal surface of the casing and the transmitter or thereceiver, a variation in the signal intensity caused by a variation inthe capacitance of an air-gap can be reduced. As a result, reliableelectric field communication can be achieved.

Preferably, in the communication apparatus, the filling member is formedof a material having a dielectric constant higher than a dielectricconstant of the casing. With this configuration, compared with a casewhere the internal surface of the casing and the transmitter or thereceiver are brought into close contact to each other without forming anair-gap therebetween, signal attenuation can be reduced, thus achievingan excellent communication state.

Preferably, in the communication apparatus, at least one of thetransmitter and the receiver accommodated in the casing includes anelectrode arranged so as to face an internal surface of the casing withthe filling member arranged therebetween. In addition, preferably, partof the internal surface of the casing includes a thin wall portion. Withthis configuration, since the volume ratio of the filling member can beincreased, signal attenuation can be reduced efficiently.

Preferably, in the communication apparatus, at least one of thetransmitter and the receiver accommodated in the casing includes anelectrode arranged so as to face an internal surface of the casing withthe filling member arranged therebetween. In addition, preferably, thefilling member is filled in an opening formed in the casing. With thisconfiguration, since the volume ratio of the filling member can beincreased, signal attenuation can be reduced efficiently.

Preferably, in the communication apparatus, the transmitter is providedin the casing.

Since a communication apparatus according to an aspect of the presentinvention includes a transmitter configured to supply an informationsignal as an electric field to a transmission medium; a receiverconfigured to detect the electric field through the transmission mediumto acquire the information signal; an insulating casing thataccommodates at least one of the transmitter and the receiver; and afilling member that is arranged at least one of between the casing andthe transmitter and between the casing and the receiver, reliableelectric field communication can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an equivalent circuit diagram of a communication system usingelectric field communication in a case where a receiver is provided in acasing;

FIG. 1B is an equivalent circuit diagram of the communication systemusing electric field communication in a case where a transmitter isprovided in a casing;

FIG. 2 is a graph showing changes in output voltage when the spacebetween the internal surface of the casing and a transmission electrodeof the transmitter and the space between the internal surface of thecasing and a reception electrode of the receiver are changed;

FIG. 3 illustrates an apparatus main body of a communication apparatusaccording to an embodiment of the present invention;

FIG. 4 is a cross-sectional view of the apparatus main body taken alongline IV-IV of FIG. 3;

FIGS. 5A to 5D are illustrations showing other examples of acommunication apparatus according to an embodiment of the presentinvention; and

FIG. 6 is a characteristic diagram showing the relationship between thecommunication speed and the distance between an electrode and a humanbody.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to the accompanying drawings.

As described above, in a case where a transmitter or a receiver isprovided in the casing of an electronic apparatus such as a cellularphone, when a space is formed between the internal surface of the casingand a transmission electrode of the transmitter or between the internalsurface of the casing and a reception electrode of the receiver, anunstable capacitance is formed. FIGS. 1A and 1B illustrate equivalentcircuits of a communication system using electric field communication.FIG. 1A is an equivalent circuit diagram in a case where a receiver isprovided in a casing. FIG. 1B is an equivalent circuit diagram in a casewhere a transmitter is provided in a casing.

Referring to FIGS. 1A and 1B, a capacitance Ct is formed between atransmitter 1 and a human body 2 serving as a transmission medium, and acapacitance Cr is formed between a receiver 3 and the human body 2. Inaddition, a capacitance Chg is formed between the human body 2 and theground, and a capacitance Cx, which is an unstable series capacitance,is formed between the internal surface of the casing and a transmissionelectrode of the transmitter or between the internal surface of thecasing and a reception electrode of the receiver.

In a case where the receiver 3 is provided in the casing of theelectronic apparatus, the unstable series capacitance Cx is formedbetween the internal surface of the casing and the reception electrodeof the receiver 3, as shown in FIG. 1A. For example, in a case where thereception electrode of the receiver 3 has an area of 4 squarecentimeters (2 cm×2 cm) and the casing accommodating the receiver 3 isformed of an acrylonitrile butadiene styrene (ABS) resin having arelative dielectric constant of 3 and a thickness of about 0.3 mm, whenthe capacitance Chg is assumed to be 110 pF (it is assumed that the feetare fixed to the ground) and the detected capacitance at the receiver 3is 1 pF, the unstable series capacitance Cx formed in a space of 1 mm orless between the internal surface of the casing and the receptionelectrode of the receiver 3 is 3 pF or more.

Meanwhile, in a case where the transmitter 1 is provided in the casingof the electronic apparatus, the unstable series capacitance Cx isformed between the internal surface of the casing and the transmissionelectrode of the transmitter 1, as shown in FIG. 1B. For example, in acase where the transmission electrode of the transmitter 1 has an areaof 4 square centimeters (2 cm×2 cm) and the casing accommodating thetransmitter 1 is formed of an ABS resin having a relative dielectricconstant of 3 and a thickness of about 0.3 mm, when the capacitance Chgis assumed to be 110 pF (it is assumed that the feet are fixed to theground) and the detected capacitance at the transmitter 1 is 1 pF, theunstable series capacitance Cx formed in a space of 1 mm or less betweenthe internal surface of the casing and the transmission electrode of thetransmitter 1 is 3 pF or more.

The inventors of the present invention have focused on the fact that ina case where a transmitter or a receiver for electric fieldcommunication is provided in an electronic apparatus, when a space(air-gap) is formed between a transmission electrode of the transmitterand the internal surface of the casing of the electronic apparatus orbetween a reception electrode of the receiver and the internal surfaceof the casing of the electronic apparatus, an unstable seriescapacitance is formed, which inhibits reliable electric fieldcommunication. Then, the inventors have found that by filling theair-gap formed between the transmission electrode or the receptionelectrode and the internal surface of the casing with a dielectricmaterial, the unstable series capacitance can be eliminated and reliableelectric field communication can thus be achieved, and have made thepresent invention based on the finding.

That is, the gist of the present invention is to achieve more reliableelectric field communication using a communication apparatus including atransmitter configured to supply an information signal as an electricfield to a transmission medium; a receiver configured to detect theelectric field through the transmission medium to acquire theinformation signal; an insulating casing that accommodates at least oneof the transmitter and the receiver; and a filling member that isarranged at least one of between the casing and the transmitter andbetween the casing and the receiver.

Under the conditions shown in FIGS. 1A and 1B, changes in output voltagewhen the space between the internal surface of the casing and thetransmission electrode of the transmitter and the space between theinternal surface of the casing and the reception electrode of thereceiver were changed were examined. FIG. 2 shows the result of theexamination. As is clear from FIG. 2, when a space exists between theinternal surface of the casing and the transmission electrode of thetransmitter, the space greatly affects output voltage, and thus greatlyaffects communication. Hence, with the configuration according to anembodiment the present invention, a higher advantage can be achievedwhen a transmitter is provided in the casing of an electronic apparatus.

Now, a system in which electric field communication is performed will beexplained. This system mainly includes a transmission medium, such as ahuman body, for transmitting an information signal through an electricfield; a transmitter configured to supply the information signal as theelectric field to the transmission medium; and a receiver configured todetect the electric field through the transmission medium and receivethe electric field to acquire the information signal. In this system,electrical capacitive coupling is formed through a capacitor between thetransmitter and the transmission medium (for example, a human body) anda capacitor between the receiver and the transmission medium, and aninformation signal is converted into an electric field and thentransmitted through the transmission medium. In this case, since not astationary current but a displacement current flows to the transmissionmedium, it is not necessary to establish electric conduction of thetransmission medium. Hence, since, for example, even when thetransmitter is placed in a pocket, the capacitive coupling between thetransmitter and the transmission medium can be formed with a thin clothlocated therebetween, transmission of an information signal can berealized.

The transmitter temporarily modulates an information signal in apredetermined modulation method and supplies the modulated informationsignal as an electric field to the transmission medium. To this end, thetransmitter includes a modulation circuit configured to modulate acarrier wave using the information signal; a conversion circuitconfigured to amplify the modulated signal and convert the amplifiedsignal into a voltage change; and a transmission electrode configured tosupply an electric field to the transmission medium.

The receiver detects the electric field through the transmission mediumto acquire the information signal. The receiver includes a receptionelectrode configured to receive an electric field from the transmissionmedium, the reception electrode facing the transmission medium; adetection circuit configured to amplify and detect the electric field;and a demodulation circuit configured to demodulate the modulatedinformation signal by using the detected physical quantity.

In a case where electric field communication is performed in the systemhaving the configuration described above, the transmitter modulates,using an information signal, a carrier wave having a frequency (within arange from several tens of kHz to several tens of MHz) at which thehuman body exhibits conductivity. The modulated information signal isamplified and then converted into a voltage change. By applying thevoltage change to the electrode of the transmitter, an electric fieldcorresponding to the modulated information signal is generated near theelectrode. Then, the electric field is applied to a human body. Theelectric field applied to the human body is received at the receptionelectrode of the receiver. When the electric field is applied to thereception electrode, the detection circuit detects the modulatedinformation signal. Then, the demodulation circuit, which is provideddownstream the detection circuit, performs demodulation using thecarrier wave used in the transmitter to obtain the original informationsignal. As described above, transmission and reception of an informationsignal can be performed through a human body serving as a transmissionmedium. Various modulation methods, such as amplitude modulation (AM),frequency modulation (FM), amplitude-shift keying (ASK), phase-shiftkeying (PSK), and quadrature shift keying (QSK), may be used as themodulation method described above.

A communication apparatus according to an embodiment of the presentinvention has a configuration in which a transmitter or a receiver for asystem in which the electric field communication described above isperformed is provided in the casing of an apparatus main body 11 shownin FIG. 3. The apparatus main body 11 includes a display 12 and anoperation buttons 13. FIG. 4 is a cross-sectional view of the apparatusmain body 11 taken along line IV-IV of FIG. 3. Referring to FIG. 4, atransmitter is provided in an insulating casing 21. The transmittermainly includes a transmission electrode 22 and circuit boards 23.Specifically, the transmission electrode 22 is provided on the internalsurface of the casing 21 with a filling member 24 arranged therebetween.In addition, the circuit boards 23 are provided on the transmissionelectrode 22 with spacers 25 arranged therebetween. The transmissionelectrode 22 is electrically connected to the circuit boards 23. Asdescribed above, with the configuration shown in FIG. 4, in a case wherethe transmitter is provided in the casing 21, a space formed between theinternal surface of the casing 21 and the transmission electrode 22 isfilled with the filling member 24, so that an unstable capacitance isprevented from being formed between the internal surface of the casing21 and the transmission electrode 22. Consequently, electric field lossbetween the internal surface of the casing 21 and the transmissionelectrode 22 can be reduced to as small as possible.

Since, as described above, the filling member 24 is placed between theinternal surface of the casing 21 and the transmission electrode 22, theelectrostatic capacitance between the transmission electrode or thereception electrode and the transmission medium increases, thus reducingsignal attenuation. Furthermore, since no air-gap is formed between theinternal surface of the casing 21 and the transmission electrode 22, avariation in the signal intensity caused by a variation in thecapacitance of an air-gap can be reduced. Consequently, reliableelectric field communication can be achieved.

It is desirable that a high dielectric material having a relatively highdielectric constant be used as a material of the filling member 24. Forexample, adhesives, such as an epoxy adhesive (a relative dielectricconstant within a range from 2.5 to 6), an acrylic adhesive (a relativedielectric constant within a range from 2.7 to 4.5), a silicone adhesive(a relative dielectric constant within a range from 3.5 to 5), and aurethane adhesive (a relative dielectric constant within a range from6.5 to 7.1); rubbers, such as a silicone rubber (a relative dielectricconstant within a range from 3 to 3.5); resins, such as, an ABS resin (arelative dielectric constant within a range from 2.4 to 4.1) and aurethane resin (a relative dielectric constant within a range from 6.5to 7.1); and the like may be used as high dielectric constant materials.

In addition, it is desirable that the filling member 24 be formed of amaterial having a dielectric constant higher than the dielectricconstant of the casing 21. With this arrangement, signal attenuation canbe reduced and an excellent communication state can be achieved comparedwith a case where the internal surface of the casing 21 and thetransmission electrode 22 are brought into close contact to each otherwithout forming an air-gap therebetween. For example, in a case wherethe casing 21 is formed of an ABS resin having a relative dielectricconstant of 3, a material having a relative dielectric constant of 4 ormore is selected as a material of the filling member 24.

In addition, a conductive material having a relatively high conductivitymay be used as a material of the filling member 24. For example,conductive adhesives, such as an epoxy conductive adhesive and apolyimide conductive adhesive, a silver paste, and the like may be usedas high-conductivity materials.

FIGS. 5A to 5D are illustrations showing other examples of acommunication apparatus according to an embodiment of the presentinvention. Referring to FIGS. 5A and 5B, the transmission electrode 22of the transmitter accommodated in the casing 21 faces the internalsurface of the casing 21 and part of the internal surface of the casing21 includes a thin wall portion 21 a. The filling member 24 is filled inan area including the thin wall portion 21 a. That is, the thin wallportion 21 a is provided on the internal surface of the casing 21, andthe transmission electrode 22 is provided on the internal surface of thecasing 21 with the filling member 24 arranged therebetween in the areaincluding the thin wall portion 21 a. As described above, since the thinwall portion 21 a is provided in the area of the casing 21 that facesthe transmission electrode 22 and the filling member 24 is filled in thethin wall portion 21 a, the volume ratio of the filling member 24 can beincreased, thereby efficiently reducing signal attenuation.

Referring to FIG. 5C, the transmission electrode 22 of the transmitteraccommodated in the casing 21 faces the internal surface of the casing21 and the internal surface includes an opening 21 b. The filling member24 is filled in the opening 21 b, and the filling member 24 is exposedto the outside of the casing 21. That is, the opening 21 b is providedin the casing 21, and the transmission electrode 22 is provided on theinternal surface of the casing 21 with the filling member 24 arrangedtherebetween in the opening 21 b. As described above, since the opening21 b is provided in the area of the casing 21 that faces thetransmission electrode 22 and the filling member 24 is filled in theopening 21 b, the volume ratio of the filling member 24 can beincreased, thereby efficiently reducing signal attenuation.

In a case where the filling member 24 is filled in the opening 21 b,when a conductive material is used as a material of the filling member24, it is not necessary to cause the transmission electrode 22 and ahuman body serving as a transmission medium to be brought intoconduction with each other. Thus, as shown in FIG. 5D, the fillingmember 24 formed of a conductive material may be covered with aninsulating material 26.

An example performed in order to clarify advantages of the presentinvention will be explained.

Data communication was performed using electric field communicationwhile a material arranged between a transmission electrode of atransmitter and a human body phantom (model) was changed, and areduction in the communication speed according to the distance betweenthe transmission electrode and the human body phantom was examined. Inaddition, a reduction in the communication speed according to thedistance between a reception electrode of a receiver and the human bodyphantom was also examined. FIG. 6 shows the examination results. Thecommunication speed was measured at a carrier frequency of 10 MHz and asignal amplitude of 1 Vp-p. For the ordinate of FIG. 6, standardizationwas performed by setting the communication speed when the electrodes andthe human body phantom were in close contact to each other to 100%.

As is clear from FIG. 6, even an air-gap of about 0.5 mm formed betweenthe reception electrode and the human body phantom did not affect thecommunication speed. Concerning an air-gap formed between thetransmission electrode and the human body phantom, the communicationspeed reduced to 44% in the case of an air-gap of 0.02 mm, reduced to17% in the case of an air-gap of 0.05 mm, and reduced to 8% in the caseof an air-gap of 0.1 mm (see the characteristic curve of air (a relativedielectric constant of 1) in FIG. 6). Meanwhile, by arranging an ABSresin having a relative dielectric constant of 3 between thetransmission electrode and the human body phantom, the communicationspeed recovered from 17% to 53% in the case of an air-gap of 0.05 mm,and recovered from 8% to 27% in the case of an air-gap of 0.1 mm. Inaddition, by arranging a urethane resin having a relative dielectricconstant of 7 between the transmission electrode and the human bodyphantom, the communication speed recovered from 17% to 100% in the caseof an air-gap of 0.05 mm, and recovered from 8% to 62% in the case of anair-gap of 0.1 mm. As described above, by arranging a filling memberbetween an electrode and a human body phantom, the communication speedwas prevented from being reduced, and stabilization of electric fieldcommunication was thus achieved. In particular, it was found that ahigher effect can be achieved by using a material having a highdielectric constant as a material of the filling member.

The present invention is not limited to the embodiment described aboveand various changes can be made to the present invention. For example,although the case where a transmitter is provided in the casing of anapparatus main body has been explained in the foregoing embodiment, thepresent invention is not limited to this. The present invention can alsobe applied in a similar manner to the case where a receiver is providedin the casing of an apparatus main body. In addition, sizes, values, andthe like set in the foregoing embodiment are not particularly limited.The sizes, values, and the like can be changed within the range of thepresent invention. Furthermore, various changes can be made to thepresent invention in an appropriate manner without departing from thescope of the present invention.

1. A communication apparatus comprising: a transmitter configured tosupply an information signal as an electric field to a transmissionmedium; a receiver configured to detect the electric field through thetransmission medium to acquire the information signal; an insulatingcasing that accommodates at least one of the transmitter and thereceiver; and a filling member that is arranged at least one of betweenan internal surface of the casing and the transmitter accommodated inthe casing and between the internal surface of the casing and thereceiver accommodated in the casing, wherein at least one of thetransmitter and the receiver accommodated in the casing includes anelectrode arranged so as to face the internal surface of the casing,wherein the filling member fills a gap between the electrode and theinternal surface of the casing, and wherein part of the casing facingthe electrode includes a thin wall portion such that a volume ratio ofthe filling member with respect to the casing between the electrode andthe internal surface is increased.
 2. The communication apparatusaccording to claim 1, wherein the filling member is formed of a materialhaving a dielectric constant higher than a dielectric constant of thecasing.
 3. The communication apparatus according to claim 1, wherein thetransmitter is provided in the casing.
 4. The communication apparatusaccording to claim 1, wherein the filling member further fills anopening formed in the casing.
 5. The communication apparatus accordingto claim 1, wherein the receiver is provided in the casing.
 6. Areceiver that detects an electric field through a transmission medium toacquire an information signal, comprising: a receiver circuit and anelectrode; an insulating casing that accommodates the receiver circuitand the electrode; and a filling member that is arranged between aninternal surface of the casing and the electrode, wherein the electrodeis arranged so as to face the internal surface of the casing; whereinthe filling member fills a gap between the electrode and the internalsurface of the casing, and wherein part of the casing facing theelectrode includes a thin wall portion such that a volume ratio of thefilling member with respect to the casing between the electrode and theinternal surface is increased.
 7. The receiver according to claim 6,wherein the filling member is formed of a material having a dielectricconstant higher than a dielectric constant of the casing.
 8. Thereceiver according to claim 6, wherein the filling member further fillsin an opening formed in the casing.
 9. A transmitter that supplies aninformation signal as an electric field to a transmission medium,comprising: a transmitter circuit and an electrode; an insulating casingthat accommodates the transmitter circuit and the electrode; and afilling member that is arranged between an internal surface of thecasing and the electrode, wherein the electrode is arranged so as toface an internal surface of the casing, and wherein the filling memberfills a gap between the electrode and the internal surface of thecasing, and wherein part of the casing facing the electrode includes athin wall portion such that a volume ratio of the filling member withrespect to the casing between the electrode and the internal surface isincreased.
 10. The transmitter according to claim 9, wherein the fillingmember is formed of a material having a dielectric constant higher thana dielectric constant of the casing.
 11. The transmitter according toclaim 9, wherein the filling member further fills an opening formed inthe casing.
 12. The communication apparatus according to claim 1,wherein the filling member has a dielectric constant higher than adielectric constant of air so as to increase a capacitive couplingbetween the electrode and the transmission medium.
 13. The communicationapparatus according to claim 1, wherein the filling member is formed ofa material having a dielectric constant higher than a dielectricconstant of the casing such that the increased volume ratio of thefilling member increases a capacitive coupling between the electrode andthe transmission medium.
 14. The receiver according to claim 6, whereinthe filling member has a dielectric constant higher than a dielectricconstant of air so as to increase a capacitive coupling between theelectrode and the transmission medium.
 15. The receiver according toclaim 6, wherein the filling member is formed of a material having adielectric constant higher than a dielectric constant of the casing suchthat the increased volume ratio of the filling member increases acapacitive coupling between the electrode and the transmission medium.16. The transmitter according to claim 9, wherein the filling member hasa dielectric constant higher than a dielectric constant of air so as toincrease a capacitive coupling between the electrode and thetransmission medium.
 17. The transmitter according to claim 9, whereinthe filling member is formed of a material having a dielectric constanthigher than a dielectric constant of the casing such that the increasedvolume ratio of the filling member increases a capacitive couplingbetween the electrode and the transmission medium.